This invention relates to an internal combustion engine of the free piston gas generator type, in which the entire energy output of the engine assemblies resides in the products of combustion, mixed with excess scavenging air, flowing through the motor cylinders at an elevated temperature and pressure, into a common exhaust header. The hot gases so generated may be used as example in either reciprocating or rotary prime movers.
It is known that the output efficiency of the existing free piston engine is closely related to the scavenging efficiency of the power cylinder and since the scavenging takes place at the outer dead points of the piston strokes, it is obvious that the rapidity of the stroke reversals at these points directly affects scavenging efficiency.
Concequently small free piston engines with low piston inertia, possess very rapid stroke reversals with poor output efficiency, while large free piston engines with large piston inertia possess less rapid stroke reversals with a relatively good output efficiency.
For example, existing single cylinder engines of this type in the 1000 gas H.P. output range are run with an efficiency of over 40% at 600 cycles per minute, while small engines in the 50 gas H.P. output range are run with an output efficiency of 12% at best, because of excessive fouling of the combustion air with trapped exhaust gas and lost energy for high super charging.
The purpose of this invention is to overcome the scavenging handicap of the presently known free piston gas generator engine without altering its inherently good features, regardless of output range.
In order that the present invention may be fully understood, reference is made to the accompanying drawings and diagram, forming part of this specification and illustrating by way of examples some embodiments of free piston gas generators according to the present invention and wherein: